Of foams comprising three-dimensional network skeletal structure, porous molded products comprising urethane foams or the like mainly composed of open cells or from which cell membranes have been removed have spaces communicating through the inside and outside, formed by the open cells or cell-membrane-free network skeleton. Accordingly, in such porous molded products, fluids such as air and liquid can pass through said communicative spaces and on the other hand any particles larger than the cells or the mesh pores (open spaces in the network) can not pass through these cells or mesh pores and captured at the cell or mesh part. They therefore are widely used in air filters, liquid-filtering mediums, etc. Such porous molded product is also used for the purpose of depositing a ceramic to the skeleton of the porous molded product so that the ceramic may retain in a predetermined shape when the porous ceramic structural bodies to be used as catalysts or the like are sinter molded.
Incidentally, since the porous molded products have a structure that substantially spherical cells (pores) communicating to one another or a structure that membranes of the cells have been removed, the breathing resistance can be reduced by reducing the number of cells (cell number per inch), whereby pressure loss can be minimized and flow velocity of fluids can be increased.
However, by reducing the cell number of the porous molded product, the size of the open cells or the mesh pores of the skeleton becomes larger to cause the following problems.
A first problem is that minute particles can not be filtered if such porous molded product is used as a filtering medium. A second problem is that if such porous molded product is used as a starting material for a ceramics carrier, the mesh size of porous ceramic structural body to be obtained becomes larger, and therefore, in instances where such porous ceramic structural body is used as catalysts, the contact area between the fluid (gases, etc.) flowing through the inside of said ceramic structural body and the ceramic becomes smaller to reduce its catalytic action.
For this reason, in conventional cases, there has been a limit in making cell size smaller, and it has been impossible to obtain porous molded products having small pressure loss.